How Many Pounds of Chlorine to Open a Swimming Pool?

Chlorination clears out chlorine-nitrogen compounds called chloramines, which cause red eyes and skin irritation. The nitrogen mostly comes from swimmer waste--urine and sweat. Some municipalities require chlorination to open a pool to the public; others regulate them on private property. How much chlorine you need depends on the size of your pool and the condition of the water in it.

Determining the Chloramine Levels

• Chlorine is measured in parts per million when used in chemical treatments, and tests that measure both chloramines and chlorine need to be run. The standard test for this is the DPD (N, N-diethyl-p-phenylenediamine) two-part test. To perform the DPD test, you'll need two buckets of pool water. A tablet that measures the total amount of chlorine compounds--chlorine and chloramines together--is placed into one bucket. A second tablet, which only measures pure chlorine, is put into the other. Subtracting the results of the second test from the first will give you the parts per million of chloramines in your pool water. The DPD test can be purchased at any pool store.

Chlorine Dosing

• Once you know the parts per million of chloramines, add 10 times that number in parts per million of chlorine.

  Your pool has a capacity in gallons, and each gallon of water weighs 8.34 pounds. Multiply the capacity of the pool by 8.34. Then divide 1,000,000 (one million) by the number of pounds of water in the pool. This tells you how many parts per million a pound of chlorine will add. From there, use the results of your test to determine how many pounds of chlorine to add. The percentage of chlorine you'll get from a given treatment will vary by the compound used, but ranges from 100% (for chlorine gas) to 56% for most of the easily used salt soluble products. Divide the number of pounds of chlorine needed by the percentage of available chlorine in the compound you're using to find out how many pounds are needed.

Example

• Let's assume a 12,000 gallon pool with a 2 ppm chloramine problem. 12,000 gallons times 8.34 is 100,080 pounds of water. 1,000,000 divided by 100,080 is 9.9999. We'll call that 1 pound of chlorine to get 10 ppm. We need to get 20 ppm of chlorine into the pool to remove the chloramines. This means we need 2 pounds of chlorine. The compound we're using is 65% cal-chloride, which means that we need 2 divided by 0.65, or 3.07 pounds of the compound (which is close enough to three pounds; an ounce won't make a difference).